Conventionally, there is known a gas concentration estimation apparatus that estimates concentration of a target component in an analyte gas by analyzing a light emitted from plasma of the analyte gas. For example, Japanese Unexamined Patent Application Publication No. 1997-304280 discloses a gas concentration estimation apparatus of this kind.
More particularly, Japanese Unexamined Patent Application Publication No. 1997-304280 discloses a concentration measuring method of carbon dioxide by means of the laser induced fluorescence method. The above described concentration measuring method causes a carbon dioxide molecule to absorb a plurality of photons at once in view of the fact that it is hard to acquire a laser capable of exciting a carbon dioxide molecule to a target energy level with absorption of one photon.